1. Field of the Invention
The present invention relates generally to an electric bicycle, and more particularly to an electric auxiliary apparatus for a bicycle.
2. Description of the Related Art
A conventional electric bicycle generally comprises a high speed electric motor used as an auxiliary power source, a gear reduction mechanism for reducing the speed of the electric motor and increasing the output torque from the electric motor, and a power combining mechanism for combining the electric power from the electric motor after speed reduction and the pedaling power from the bracket axle by the rider. The combined driving power drives a chain wheel at the bracket axle for driving the electric bicycle. Accordingly, the force and the power required from the rider for driving the bicycle are relatively reduced. A pedal force sensor is generally provided in a pedal force transmission path to detect the magnitude of the pedal force for controlling the output power from the auxiliary electric motor in accordance with the pedal power.
U.S. Pat. No. 5,341,892 entitled "Motor and Driven Bicycle" discloses a power combination mechanism mainly including bearing-type single-direction clutches, and a pedal force sensing mechanism using a planar cam and a compression spring to create an anal displacement, which, in turn, is detected by an induction coil means for outputting a signal corresponding to the magnitude of the pedal force. R.O.C. Publication No. 289327 discloses an electric bicycle comprising a power combination mechanism primarily consisting of a bearing-type single-direction clutch and a ratchet-wheel type single-direction clutch, and a pedal force sensing mechanism using a planetary gear and a compression spring to create an absolute angular displacement, which, in turn, is detected by a revolving potential meter for outputting a signal corresponding to the magnitude of the pedal force. R.O.C. Publication No. 276299 discloses an electric bicycle comprising a power combination mechanism primarily consisting of two single-direction clutches, and a pedal force sensing mechanism using a torque rod to create a relative angular displacement further amplified by a lever, which, in turn, is detected by a linear potential meter for outputting a signal corresponding to the magnitude of the pedal force.
Generally speaking, the power combination mechanisms of the above conventional electric bicycles utilize a pair of single-direction clutches (i.e., single-direction bearing or ratchet-wheel clutches) to combine the motor power and pedal power. When riding, if the rotational speed of pedaling is higher than that of the motor after gear reduction, the pedal force solely drives the bicycle under the action of the single direction clutch and the inertia of the elements of the motor do not become a burden for pedaling; if the rotational speed of the motor after gear reduction is higher than that of pedaling, the motor power solely drives the bicycle under the action of the single direction clutch and the inertia of the elements of the pedaling mechanism do not become a burden for the electric motor, and if the rotational speed of the motor after gear reduction is synchronized with that of pedaling, the pedal force and the motor power are combined together to drive the bicycle. Therefore, unless the rotational speed of the motor after gear reduction is accurately synchronized with that of pedaling, there is only one power source being utilized for driving the bicycle, thereby resulting in wastage of energy. An additional sensing mechanism for rotational speed and controlling apparatus is required for the power combination mechanisms in order to synchronize the rotational speed of the motor after gear reduction with that of pedaling, thereby resulting in a more complicated structure and higher cost for the power combination mechanisms.
Further, the elements of the pedal force sensing mechanism of the above conventional electric bicycles use a torque rod or a planar cam to transfer the relative angular displacement to an axial displacement which, in turn, is detected in a close-contact sensing means for outputting a signal corresponding to the magnitude of the pedal force. Since the pedal force sensing mechanism is located in the pedal force transmission path, the elements thereof are liable to wear.
The present invention is intended to provide an electric auxiliary apparatus for a bicycle that mitigates and/or obviates the drawbacks of the above conventional electric bicycle.